This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Binocular alignment must be maintained in the horizontal, vertical and torsional planes to ensure binocular sensory fusion. Unfortunately, abnormal visual experience during development usually leads to ocular misalignment (strabismus). In fact, various studies have reported the incidence of strabismus to be about 2-5% of the infant population. We have developed an animal model for strabismus by rearing monkeys that only view the world through one eye at a time. This is accomplished by placing an opaque contact lens on one eye and alternating to the other eye on a daily basis (alternate monocular occlusion) for the first few months of life. Our data from strabismic monkeys are similar to human data showing that ocular misalignment is accompanied by a lack of binocular coordination. In addition to horizontal misalignment, we have found that the animals show vertical misalignment with the non-fixating eye being higher than the fixating eye. Both horizontal and vertical misalignment varies with gaze position. Thus our rearing paradigm of alternate monocular occlusion produces animals with alignment patterns that resemble human forms of strabismus such as A/V pattern strabismus and Dissociated Vertical Deviation (DVD). These phenomena are incompletely understood and we are conducting neurophysiological and behavioral studies to study them. We previously showed that neuronal drive from motoneurons was responsible for determining the state of eye misalignment in animals with a sensory form of strabismus. New data shows that pre-motor areas in the midbrain relating to control of vergence and ocular accommodation might play a role in the development and maintenance of strabismus. Completion of our studies will be of benefit to the understanding and treatment of certain types of strabismus.